Basically if you have a stack of lets say 500 fuel, then the inventory of the station got 25 fuel in a stack, then you first drag the fuel stack down to the other stack. Add them to the stack and rescind the order with the other mouse button you will not only sell that amount of fuel but you will also get the same amount you sold and what you still got in your hand back into your inventory, so you still got 500 fuel but the stack in the station has turned either 500 or 499. Its a sure way to get cash fast and to multiply the amount of fuel around by a lot, just thought i would tip it seeing as its such a great income source, especially if you start with the fuel ship and i suppose its not a mechanic meant to be there:)
